The present invention relates to an optical module having a reduced diameter structure in which an optical semiconductor element of the cap sealing type is butted and joined to a housing containing an optical part in a state that an optical optimal position relation holds therebetween.
An optical module is a device in which an optical semiconductor element (such as a semiconductor light emitting device, e.g., a laser diode or a semiconductor light receiving (detecting) device, e.g., a photo diode) and an optical part (such as a lens and an optical fiber ferule) are held while being aligned with each other. An array module (an optical module unit) is also available, in which a plurality of such optical modules are arrayed.
An optical module used in the optical communications field includes, for example, an optical semiconductor element (an optical semiconductor device), a lens, and a housing which holds the optical semiconductor element and the lens, and fittingly receives a ferule of an optical plug of a mating connecting member. When the optical plug is connected thereto, the optical semiconductor element is optically coupled with the optical fiber of the ferule through the lens. The optical coupling to the optical fiber is usually based on a mechanical structure constructed according to the standard on various optical connectors.
A spherical lens is widely used for the lens assembled into the optical module for the following reasons. It is manufactured highly accurately by only machining work. This results in cost reduction of the product. Further, it has no directivity. Because of this, in assembling the lens, there is no need for its orientation adjustment, and hence the assembling work is easy. An aspherical lens, a gradient index rod lens or the like is also used for the lens of the optical module. A metallic housing was widely used for the housing for holding the optical semiconductor element and the lens. In recent days, a resin housing is frequently used for the same for the following reasons. The resin housing allows the lens to be put thereinto by insert molding. Alternatively, the lens can be held with a plurality of pawl-like protruded pieces. Accordingly, the manufacturing is smooth and easy, and the cost to manufacture is reduced. The optical semiconductor element widely used is of the so-called cap sealing structure type in which an element body is sealingly mounted within a cap having a window.
In the usual manufacturing of the optical module, the optical semiconductor element, the lens and the optical fiber are aligned with one another in an optically optimal position relationship, and then the optical semiconductor element is fastened to the housing containing the lens. In a case where the optical semiconductor element is a laser diode, the laser diode is driven to emit laser light, the laser light is input to the optical fiber, and the laser light emitted from the optical fiber is monitored. At a position where the outgoing laser light is maximized in intensity, the optical semiconductor element is fastened to the housing.
In the optical module using the optical semiconductor element of the cap sealing type, the housing is designed so that the cap of the optical semiconductor element is insertable into the housing, and accordingly, the stem part of the optical semiconductor element is joined to the end face of the housing. In a case where the housing is made of resin, any of various types of adhesives may be used for the bonding, and where it is made of a metallic material, the YAG welding is often used for the bonding. In either case, those are joined together in a state that the side surface of the cap of the optical semiconductor element is entirely covered with a part of the housing.
Recently, with increase of optical communications capacity, the need of mounting the optical fibers at high density increases in the optical transmission device and the like. Accordingly, further size reduction of the optical module mounted thereon is also required. Specifically, the market demands the development of the optical module which is adaptable for the LC, MU and other types of small optical connectors, while the conventional optical module is satisfactory if it is adaptable for the SC type connector.
In the optical module using the optical semiconductor element of the cap sealing type, the outer diameter of the optical module is inherently larger than the diameter of the stem part of the optical semiconductor element. In this respect, limitation is put on the size and diameter reduction of the optical module.
Accordingly, an object of the present invention is to provide a small optical module.
Another object of the invention is to provide an optical module which is adaptable for the small optical connectors of the LC, MU and the like type.
Yet another object of the invention is to provide a small optical module which is readily applied to the optical module of the tablet type or the like.
According to an aspect of the present invention, there is provided an optical module in which an optical semiconductor element of the cap sealing type is mounted on a housing to be aligned with an optical axis of an optical part contained in the housing. The optical module is characterized in that the upper surface of a cap of the optical semiconductor element is bonded to the end face of the housing. With such a construction, the maximum outer diameter of the optical module can be within the maximum outer diameter of the optical semiconductor element.
Examples of the optical parts contained within the housing include a lens and an optical fiber ferule. The optical part contained within the housing may be not only a single optical part but also a plurality of optical parts. The housing may be structured to contain only the lens. The housing may have a structure for fittingly receiving a ferule of an optical plug of a mating connecting member, in addition to the lens built-in structure. In the latter case, the cap sealing type optical semiconductor element is aligned with the optical axes of the lens and the ferule, and then fixedly mounted on the housing. The present invention may be applied to the optical module of the type in which the optical semiconductor element is directly bonded to the ferule bore. Usually, the housing is made of synthetic resin. Ultraviolet curing adhesive is preferably used for joining the upper surface of the cap of the optical semiconductor element to the housing. Any other suitable adhesive may be used for the joining, as a matter of course.
In the optical module, the surface of the cap of the optical semiconductor element and at least a part of the side surface of the housing may be covered with a casing, and a clearance formed therebetween may be sealed with resin. In the optical module thus structured, it is preferable that the upper surface of the cap of the optical semiconductor element and the end face of the housing are bonded by ultraviolet curing adhesive, and a clearance between the inner surface of the casing, and the side surface of the cap of the optical semiconductor element and at least a part of side surface of the housing is sealed with thermosetting resin. Accordingly, the time taken for the bonding operation using the ultraviolet curing adhesive is extremely short. As a result, the coupling work of the optical optimal position is easy. With the sealing using the thermosetting resin, the bonding strength and the anti-weatherability are improved.
According to another aspect, there is provided an optical module wherein a plurality of optical modules constructed as described above are arrayed in juxtaposition and covered with a single casing, and a clearance formed therebetween is sealed with resin. A typical example of such is an optical module of the tablet type in which semiconductor light emitting elements and semiconductor light receiving elements are formed as sets in a single unit.